One of the best pieces of advice I've ever received about small business…or any business in fact:
UNDER-PROMISE AND OVER-DELIVER
You will rarely disappoint your clients, and almost always leave them feeling pleasantly surprised and satisfied with their experience with you.
Practical examples of how to apply this:
-- Set your shipping time to longer than you think it will actually be.
-- Overestimate your deadline for finishing a project. When you finish "early," it will be a pleasant surprise.
-- Leave some of the perks of a package you offer unadvertised so you can surprise your clients with it later. Maybe a free printable, access to an e-book, etc.
-- Don't oversell yourself when you're trying to make an initial deal or sale. Find a good balance between offering something people are interested in, and then providing a product or service that exceeds their expectations.